Multiple use septum for injection ports for gas chromatography or the like

A new septum for multiple use injection ports enabling the introduction of fluid materials by needle injection into a gas chromatograph or other system under positive pressure. The injection port utilizes a special septum to seal the port while accommodating passage of an injection needle. The septum is provided with an axial through passage, preferably of greater diameter than the injection needle. The septum, which is formed of elastomeric material, is placed under axial compression sufficient to inwardly displace the material surrounding the preformed opening, to tightly close and seal the opening against the pressure of the system. The septum may be penetrated multiple times by injection needles without coring or otherwise damaging the septum. Greater operating life is achieved and contamination of the system is minimized.